Encapsulated glass is one kind of safety glass, which is widely used in automobiles as front windshield glass, rear windshield glass, skylight glass or quarter window glass. Encapsulated glass may have the following advantages: 1, encapsulated glass can be bonded to a car body tightly, which guarantees sealing of the car; 2, glass is combined with encapsulating plastics in one piece, which makes it easy to install, thereby shortening the installation cycle and improving the production efficiency; meanwhile, encapsulated glass may have different types of cross section, which can be designed to make a car more aesthetic.
Encapsulated glass may be fabricated as follows. First, a piece of normal annealed glass is pre-processed such as by cutting, edging and cleaning. Second, the pre-processed annealed glass is transferred to a production line for toughening treatment, so as to obtain a piece of toughened glass. Then, an encapsulation mold, including an upper mold and a lower mold, is provided. The toughened glass is placed as an insert on a chuck of the lower mold, and is fixed with a positioning device of the lower mold. Then the upper mold and the lower mold are jointed together. Through a sprue gate, molten plastics are injected towards edges of the toughened glass. An encapsulated glass is obtained after the molten plastics are solidified and encapsulate the edges of the toughened glass.
From above, for a given toughened glass, quality of an encapsulated glass mainly depends on the encapsulating process, in which an encapsulation mold plays a critical role to ensure the quality of the encapsulating process. While injection molding is performed on the toughened glass, the toughened glass may move under huge impacts, which in turn causes the toughened glass to be crushed or scratched. Accordingly, a clamping device, which is disposed in the encapsulation mold, is needed to prevent the toughened glass from moving. Currently, a movable lifter is usually used as the clamping device.
FIG. 1 schematically illustrates a piece of glass fixed by a movable lifter. Referring to FIG. 1, a glass 1 which is to be encapsulated has a convex surface 11 (namely, an upper surface of the glass 1) and a concave surface 12 (namely, a lower surface of the glass 1), which are disposed opposite to each other. A movable lifter 2 is disposed on a lower mold (not shown). The glass 1 may be fixed in an encapsulation mold (not shown) according to the following steps. The glass 1 is firstly placed on the movable lifter 2, which brings the concave surface 12 into contact with the movable lifter 2. After that, the glass 1 is positioned preliminarily. Then an upper mold (not shown) is pressed against the lower mold. The movable lifter 2 applies a first upward force to the concave surface 12, while the upper mold applies a second downward force to the convex surface 11. Under the combined actions of the first upward force and the second downward force, the glass 1 is clamped between the movable lifter 2 and the upper mold, which may prevent the glass 1 from moving during injection molding.
To enable the glass 1 to bear huge impacts during injection molding, the position of the movable lifter 2 can be adjusted up and down. The movable lifter 2 is made of iron and is hard. The movable lifter 2 has a convex surface corresponding to the concave surface 12 of the glass 1. Most part of the concave surface 12 of the glass 1 is propped by the convex surface of the movable lifter 2, when they are brought into contact. During injection molding, a chamber of the encapsulation mold needs to be kept in a pressure maintaining state, so as to make the plastic material encapsulate edges of the glass 1 tightly. Under the actions of the pressure, the glass 1 and the movable lifter 2 squeeze each other. Because both the glass 1 and the movable filter 2 are rigid, the glass 1 may get crushed.
In addition, glasses from different batches may have different curvature tolerances. If the glass 1 has a large curvature tolerance, the concave surface 12 of the glass 1 may not match the convex surface of the movable lifter 2 well. In this case, most of pressure may concentrate on a certain point of the glass 1, which thereby may cause the glass 1 to be crushed by the movable lifter 2. Especially, when the glass 1 has a big size, a central region of the glass 1 may have a very large curvature tolerance, which may result in high breakage rate of the glass.